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For the episode of the television series The Americans, see Arpanet (The Americans).

ARPANET
ARPANET logical map, March 1977
TypeData
LocationUnited States, United Kingdom, Norway
ProtocolsLayers 1-3: 1822 protocol (IMP-host), internal/undocumented (IMP-IMP)
Layers 4+: NCP, later TCP/IP
OperatorFrom 1975, Defense Communications Agency
Established1969; 56 years ago (1969)
Closed1990; 35 years ago (1990)
Commercial?No
FundingFrom 1966, Advanced Research Projects Agency (ARPA)
ARPANET access points in the 1970s
Internet history timeline

Early research and development:

Merging the networks and creating the Internet:

Commercialization, privatization, broader access leads to the modern Internet:

Examples of Internet services:

The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first computer networks to implement the TCP/IP protocol suite. Both technologies became the technical foundation of the Internet. The ARPANET was established by the Advanced Research Projects Agency (now DARPA) of the United States Department of Defense.[1]

Building on the ideas of J. C. R. Licklider, Bob Taylor initiated the ARPANET project in 1966 to enable resource sharing between remote computers.[2] Taylor appointed Larry Roberts as program manager. Roberts made the key decisions about the request for proposal to build the network.[3] He incorporated Donald Davies' concepts and designs for packet switching,[4][5] and sought input from Paul Baran on dynamic routing.[6] In 1969, ARPA awarded the contract to build the Interface Message Processors (IMPs) for the network to Bolt Beranek & Newman (BBN).[7][8] The design was led by Bob Kahn who developed the first protocol for the network. Roberts engaged Leonard Kleinrock at UCLA to develop mathematical methods for analyzing the packet network technology.[6]

The first computers were connected in 1969 and the Network Control Protocol was implemented in 1970, development of which was led by Steve Crocker at UCLA and other graduate students, including Jon Postel.[9][10][11] The network was declared operational in 1971. Further software development enabled remote login and file transfer, which was used to provide an early form of email.[12] The network expanded rapidly and operational control passed to the Defense Communications Agency in 1975.

Bob Kahn moved to DARPA and, together with Vint Cerf at Stanford University, formulated the Transmission Control Program for internetworking.[13] As this work progressed, a protocol was developed by which multiple separate networks could be joined into a network of networks; this incorporated concepts pioneered in the French CYCLADES project directed by Louis Pouzin. Version 4 of TCP/IP was installed in the ARPANET for production use in January 1983 after the Department of Defense made it standard for all military computer networking.[14][15]

Access to the ARPANET was expanded in 1981 when the National Science Foundation (NSF) funded the Computer Science Network (CSNET). In the early 1980s, the NSF funded the establishment of national supercomputing centers at several universities and provided network access and network interconnectivity with the NSFNET project in 1986. The ARPANET was formally decommissioned in 1990, after partnerships with the telecommunication and computer industry had assured private sector expansion and commercialization of an expanded worldwide network, known as the Internet.[16]

Inspiration

[edit]

Historically, voice and data communications were based on methods of circuit switching, as exemplified in the traditional telephone network, wherein each telephone call is allocated a dedicated end-to-end electronic connection between the two communicating stations. The connection is established by switching systems that connected multiple intermediate call legs between these systems for the duration of the call.

The traditional model of the circuit-switched telecommunication network was challenged in the early 1960s by Paul Baran at the RAND Corporation, who had been researching systems that could sustain operation during partial destruction, such as by nuclear war. He developed the theoretical model of distributed adaptive message block switching.[17] However, the telecommunication establishment rejected the development in favor of existing models. Donald Davies at the United Kingdom's National Physical Laboratory (NPL) independently arrived at a similar concept in 1965.[18][19]

The earliest ideas for a computer network intended to allow general communications among computer users were formulated by computer scientist J. C. R. Licklider of Bolt Beranek and Newman (BBN), in April 1963, in memoranda discussing the concept of the "Intergalactic Computer Network". Those ideas encompassed many of the features of the contemporary Internet. In October 1963, Licklider was appointed head of the Behavioral Sciences and Command and Control programs at the Defense Department's Advanced Research Projects Agency (ARPA). He convinced Ivan Sutherland and Bob Taylor that this network concept was very important and merited development, although Licklider left ARPA before any contracts were assigned for development.[20]

Sutherland and Taylor continued their interest in creating the network, in part, to allow ARPA-sponsored researchers at various corporate and academic locales to utilize computers provided by ARPA, and, in part, to quickly distribute new software and other computer science results.[21] Taylor had three computer terminals in his office, each connected to separate computers, which ARPA was funding: one for the System Development Corporation (SDC) Q-32 in Santa Monica, one for Project Genie at the University of California, Berkeley, and another for Multics at the Massachusetts Institute of Technology. Taylor recalls the circumstance: "For each of these three terminals, I had three different sets of user commands. So, if I was talking online with someone at S.D.C., and I wanted to talk to someone I knew at Berkeley, or M.I.T., about this, I had to get up from the S.D.C. terminal, go over and log into the other terminal and get in touch with them. I said, 'Oh Man!', it's obvious what to do: If you have these three terminals, there ought to be one terminal that goes anywhere you want to go. That idea is the ARPANET".[22]

Donald Davies' work caught the attention of ARPANET developers at the Symposium on Operating Systems Principles in October 1967.[23] He gave the first public presentation, having coined the term packet switching, in August 1968 and incorporated it into the NPL network in England.[24][25] The NPL network and ARPANET were the first two networks in the world to implement packet switching.[26][27][28] Roberts said the computer networks built in the 1970s were similar "in nearly all respects" to Davies' original 1965 design.[29]

Creation

[edit]

In February 1966, Bob Taylor successfully lobbied ARPA's Director Charles M. Herzfeld to fund a network project. Herzfeld redirected funds in the amount of one million dollars from a ballistic missile defense program to Taylor's budget.[30] Taylor hired Larry Roberts as a program manager in the ARPA Information Processing Techniques Office in January 1967 to work on the ARPANET.[31] Roberts met Paul Baran in February 1967, but did not discuss networks.[32][33]

Roberts asked Frank Westervelt to explore the questions of message size and contents for the network, and to write a position paper on the intercomputer communication protocol including “conventions for character and block transmission, error checking and re-transmission, and computer and user identification."[31] In April 1967, ARPA held a design session on technical standards. The initial standards for identification and authentication of users, transmission of characters, and error checking and retransmission procedures were discussed.[34] Roberts' proposal was that all mainframe computers would connect to one another directly. The other investigators were reluctant to dedicate these computing resources to network administration. After the design session, Wesley Clark proposed minicomputers should be used as an interface to create a message switching network. Roberts modified the ARPANET plan to incorporate Clark's suggestion and named the minicomputers Interface Message Processors (IMPs).[31][35][36][37]

The plan was presented at the inaugural Symposium on Operating Systems Principles in October 1967.[38] Donald Davies' work on packet switching and the NPL network, presented by a colleague (Roger Scantlebury), and that of Paul Baran, came to the attention of the ARPA investigators at this conference.[39][23] Roberts applied Davies' concept of packet switching for the ARPANET,[40][41] and sought input from Paul Baran on dynamic routing.[42] The NPL network was using line speeds of 768 kbit/s, and the proposed line speed for the ARPANET was upgraded from 2.4 kbit/s to 50 kbit/s.[43]

By mid-1968, Roberts and Barry Wessler wrote a final version of the IMP specification based on a Stanford Research Institute (SRI) report that ARPA commissioned to write detailed specifications describing the ARPANET communications network.[37] Roberts gave a report to Taylor on 3 June, who approved it on 21 June. After approval by ARPA, a Request for Quotation (RFQ) was issued for 140 potential bidders. Most computer science companies regarded the ARPA proposal as outlandish, and only twelve submitted bids to build a network; of the twelve, ARPA regarded only four as top-rank contractors. At year's end, ARPA considered only two contractors and awarded the contract to build the network to BBN in January 1969.[26]

1969 ARPANET IMP

The initial, seven-person BBN team were much aided by the technical specificity of their response to the ARPA RFQ, and thus quickly produced the first working system. The "IMP guys" were led by Frank Heart; the theoretical design of the network was led by Bob Kahn; the team included Dave Walden, Severo Ornstein, William Crowther and several others.[44][45][46] The BBN-proposed network closely followed Roberts' ARPA plan: a network composed of small computers, the IMPs (similar to the later concept of routers), that functioned as gateways interconnecting local resources. Routing, flow control, software design and network control were developed by the BBN team.[44][47] At each site, the IMPs performed store-and-forward packet switching functions and were interconnected with leased lines via telecommunication data sets (modems), with initial data rates of 50kbit/s.[43][48][49] The host computers were connected to the IMPs via custom serial communication interfaces. The system, including the hardware and the packet switching software, was designed and installed in nine months.[26][37][50] The BBN team continued to interact with the NPL team with meetings between them taking place in the U.S. and the U.K.[51][52][53]

As with the NPL network, the first-generation IMPs were built using a rugged computer version of the Honeywell DDP-516 computer, configured with 24KB of expandable magnetic-core memory, and a 16-channel Direct Multiplex Control (DMC) direct memory access unit.[54] The DMC established custom interfaces with each of the host computers and modems. In addition to the front-panel lamps, the DDP-516 computer also features a special set of 24 indicator lamps showing the status of the IMP communication channels. Each IMP could support up to four local hosts and could communicate with up to six remote IMPs via early Digital Signal 0 leased telephone lines. The network connected one computer in Utah with three in California. Later, the Department of Defense allowed the universities to join the network for sharing hardware and software resources.

According to Charles Herzfeld, ARPA Director (1965–1967):

The ARPANET was not started to create a Command and Control System that would survive a nuclear attack, as many now claim. To build such a system was, clearly, a major military need, but it was not ARPA's mission to do this; in fact, we would have been severely criticized had we tried. Rather, the ARPANET came out of our frustration that there were only a limited number of large, powerful research computers in the country, and that many research investigators, who should have access to them, were geographically separated from them.[55]

The ARPANET used distributed computation and incorporated frequent re-computation of routing tables (automatic routing was technically challenging at the time). These features increased the survivability of the network in the event of significant interruption. Furthermore, the ARPANET was designed to survive subordinate network losses.[56][57] However, the Internet Society agrees with Herzfeld in a footnote in their online article, A Brief History of the Internet:

It was from the RAND study that the false rumor started, claiming that the ARPANET was somehow related to building a network resistant to nuclear war. This was never true of the ARPANET, but was an aspect of the earlier RAND study of secure communication. The later work on internetworking did emphasize robustness and survivability, including the capability to withstand losses of large portions of the underlying networks.[58]

Paul Baran, the first to put forward a theoretical model for communication using packet switching, conducted the RAND study referenced above.[59][17] Though the ARPANET did not exactly share Baran's project's goal, he said his work did contribute to the development of the ARPANET.[60] Minutes taken by Elmer Shapiro of Stanford Research Institute at the ARPANET design meeting of 9–10 October 1967 indicate that a version of Baran's routing method ("hot potato") may be used,[61] consistent with the NPL team's proposal at the Symposium on Operating System Principles in Gatlinburg.[62]

Later, in the 1970s, ARPA did emphasize the goal of "command and control". According to Stephen J. Lukasik, who was deputy director (1967–1970) and Director of DARPA (1970–1975):[63]

The goal was to exploit new computer technologies to meet the needs of military command and control against nuclear threats, achieve survivable control of US nuclear forces, and improve military tactical and management decision making.[64]

Implementation

[edit]

The first four nodes were designated as a testbed for developing and debugging the 1822 protocol, which was a major undertaking. While they were connected electronically in 1969, network applications were not possible until the Network Control Protocol was implemented in 1970 enabling the first two host-host protocols, remote login (Telnet) and file transfer (FTP) which were specified and implemented between 1969 and 1973.[10][11][65] The network was declared operational in 1971. Network traffic began to grow once email was established at the majority of sites by around 1973.[12]

Initial four hosts

[edit]
First ARPANET IMP log: the first message ever sent via the ARPANET, 10:30 pm PST on 29 October 1969 (6:30 UTC on 30 October 1969). This IMP Log excerpt, kept at UCLA, describes setting up a message transmission from the UCLA SDS Sigma 7 Host computer to the SRI SDS 940 Host computer

The initial ARPANET configuration linked UCLA, ARC, UCSB, and the University of Utah School of Computing. The first node was created at UCLA, where Leonard Kleinrock could evaluate network performance and examine his theories on message delay.[66][67][68] The locations were selected not only to reduce leased line costs but also because each had specific expertise beneficial for this initial implementation phase:[1]

The first successful host-to-host connection on the ARPANET was made between Stanford Research Institute (SRI) and UCLA, by SRI programmer Bill Duvall and UCLA student programmer Charley Kline, at 10:30 pm PST on 29 October 1969 (6:30 UTC on 30 October 1969).[69] Kline connected from UCLA's SDS Sigma 7 Host computer (in Boelter Hall room 3420) to the Stanford Research Institute's SDS 940 Host computer. Kline typed the command "login," but initially the SDS 940 crashed after he typed two characters. About an hour later, after Duvall adjusted parameters on the machine, Kline tried again and successfully logged in. Hence, the first two characters successfully transmitted over the ARPANET were "lo".[70][71][72] The first permanent ARPANET link was established on 21 November 1969, between the IMP at UCLA and the IMP at the Stanford Research Institute. By 5 December 1969, the initial four-node network was established.

Elizabeth Feinler created the first Resource Handbook for ARPANET in 1969 which led to the development of the ARPANET directory.[73] The directory, built by Feinler and a team made it possible to navigate the ARPANET.[74][75]

Network performance

[edit]

In 1968, Roberts contracted with Kleinrock to measure the performance of the network and find areas for improvement.[42][76] Building on his earlier work on queueing theory and optimization of message delay in communication networks,[66][67] Kleinrock specified mathematical models of the performance of packet-switched networks, which underpinned the development of the ARPANET as it expanded rapidly in the early 1970s.[26][42] Analytic methods had limitations,[77] and computer simulation studies where also employed by ARPA,[78] and at the NPL in the United Kingdom.[27][79][80]

Growth and evolution

[edit]
ARPA network map 1973

Roberts engaged Howard Frank to consult on the topological design of the network. Frank made recommendations to increase throughput and reduce costs in a scaled-up network.[81] By March 1970, the ARPANET reached the East Coast of the United States, when an IMP at BBN in Cambridge, Massachusetts was connected to the network. Thereafter, the ARPANET grew: 9 IMPs by June 1970 and 13 IMPs by December 1970, then 18 by September 1971 (when the network included 23 university and government hosts); 29 IMPs by August 1972, and 40 by September 1973. By June 1974, there were 46 IMPs, and in July 1975, the network numbered 57 IMPs. By 1981, the number was 213 host computers, with another host connecting approximately every twenty days.[1]

Support for inter-IMP circuits of up to 230.4 kbit/s was added in 1970, although considerations of cost and IMP processing power meant this capability was not actively used.

Larry Roberts saw the ARPANET and NPL projects as complementary and sought in 1970 to connect them via a satellite link. Peter Kirstein's research group at University College London (UCL) was subsequently chosen in 1971 in place of NPL for the UK connection. In June 1973, a transatlantic satellite link connected ARPANET to the Norwegian Seismic Array (NORSAR),[82] via the Tanum Earth Station in Sweden, and onward via a terrestrial circuit to a TIP at UCL. UCL provided a gateway for interconnection of the ARPANET with British academic networks, the first international resource sharing network, and carried out some of the earliest experimental research work on internetworking.[83]

1971 saw the start of the use of the non-ruggedized (and therefore significantly lighter) Honeywell 316 as an IMP. It could also be configured as a Terminal Interface Processor (TIP), which provided terminal server support for up to 63 ASCII serial terminals through a multi-line controller in place of one of the hosts.[84] The 316 featured a greater degree of integration than the 516, which made it less expensive and easier to maintain. The 316 was configured with 40 kB of core memory for a TIP. The size of core memory was later increased, to 32 kB for the IMPs, and 56 kB for TIPs, in 1973.

The ARPANET was demonstrated at the International Conference on Computer Communications in October 1972.

In 1975, BBN introduced IMP software running on the Pluribus multi-processor. These appeared in a few sites. In 1981, BBN introduced IMP software running on its own C/30 processor product.

Networking evolution

[edit]

IMP functionality

[edit]

Because it was never a goal for the ARPANET to support IMPs from vendors other than BBN, the IMP-to-IMP protocol and message format were not standardized. However, the IMPs did nonetheless communicate amongst themselves to perform link-state routing, to do reliable forwarding of messages, and to provide remote monitoring and management functions to ARPANET's Network Control Center. Initially, each IMP had a 6-bit identifier and supported up to 4 hosts, which were identified with a 2-bit index. An ARPANET host address, therefore, consisted of both the port index on its IMP and the identifier of the IMP, which was written with either port/IMP notation or as a single byte; for example, the address of MIT-DMG (notable for hosting development of Zork) could be written as either 1/6 or 70. An upgrade in early 1976 extended the host and IMP numbering to 8-bit and 16-bit, respectively.[citation needed]

In addition to primary routing and forwarding responsibilities, the IMP ran several background programs, titled TTY, DEBUG, PARAMETER-CHANGE, DISCARD, TRACE, and STATISTICS. These were given host numbers in order to be addressed directly and provided functions independently of any connected host. For example, "TTY" allowed an on-site operator to send ARPANET packets manually via the teletype connected directly to the IMP.[citation needed]

1822 protocol

[edit]

The starting point for host-to-host communication on the ARPANET in 1969 was the 1822 protocol, which defined the transmission of messages to an IMP.[85] The message format was designed to work unambiguously with a broad range of computer architectures. An 1822 message essentially consisted of a message type, a numeric host address, and a data field. To send a data message to another host, the transmitting host formatted a data message containing the destination host's address and the data message being sent, and then transmitted the message through the 1822 hardware interface. The IMP then delivered the message to its destination address, either by delivering it to a locally connected host, or by delivering it to another IMP. When the message was ultimately delivered to the destination host, the receiving IMP would transmit a Ready for Next Message (RFNM) acknowledgment to the sending, host IMP.[citation needed]

Network Control Protocol

[edit]

Unlike modern Internet datagrams, the ARPANET was designed to reliably transmit 1822 messages, and to inform the host computer when it loses a message; the contemporary IP is unreliable, whereas the TCP is reliable. Nonetheless, the 1822 protocol proved inadequate for handling multiple connections among different applications residing in a host computer. This problem was addressed with the Network Control Protocol (NCP), which provided a standard method to establish reliable, flow-controlled, bidirectional communications links among different processes in different host computers. The NCP interface allowed application software to connect across the ARPANET by implementing higher-level communication protocols, an early example of the protocol layering concept later incorporated in the OSI model.[65]

NCP was developed under the leadership of Steve Crocker, then a graduate student at UCLA. Crocker created and led the Network Working Group (NWG) which was made up of a collection of graduate students at universities and research laboratories, including Jon Postel and Vint Cerf at UCLA. They were sponsored by ARPA to carry out the development of the ARPANET and the software for the host computers that supported applications.

TCP/IP

[edit]

Stephen J. Lukasik directed DARPA to focus on internetworking research in the early 1970s. Bob Kahn moved from BBN to DARPA in 1972, first as program manager for the ARPANET, under Larry Roberts, then as director of the IPTO when Roberts left to found Telenet. Kahn worked on both satellite packet networks and ground-based radio packet networks, and recognized the value of being able to communicate across both. Steve Crocker, now at DARPA, and the leaders of British and French network projects founded the International Network Working Group in 1972 and, on Crocker's recommendation, Vint Cerf, now on the faculty at Stanford University, became its Chair.[86][87][88] This group considered how to interconnect packet switching networks with different specifications, that is, internetworking. Research led by Kahn and Cerf resulted in the formulation of the Transmission Control Program,[13] which incorporated concepts from the French CYCLADES project directed by Louis Pouzin.[89] Its specification was written by Cerf with Yogen Dalal and Carl Sunshine at Stanford in December 1974 (RFC 675). The following year, testing began through concurrent implementations at Stanford, BBN and University College London.[90] At first a monolithic design, the software was redesigned as a modular protocol stack in version 3 in 1978. Version 4 was installed in the ARPANET for production use in January 1983, replacing NCP. The development of the complete Internet protocol suite by 1989, as outlined in RFC 1122 and RFC 1123, and partnerships with the telecommunication and computer industry laid the foundation for the adoption of TCP/IP as a comprehensive protocol suite as the core component of the emerging Internet.[15]

Operation

[edit]

ARPA was intended to fund advanced research. The ARPANET was a research project that was communications-oriented, rather than user-oriented in design.[91] Nonetheless, in the summer of 1975, operational control of the ARPANET passed to the Defense Communications Agency.[1] At about this time, the first ARPANET encryption devices were deployed to support classified traffic. The ARPANET Completion Report, written in 1978 and published in 1981 jointly by BBN and DARPA,[92] concludes that:

... it is somewhat fitting to end on the note that the ARPANET program has had a strong and direct feedback into the support and strength of computer science, from which the network, itself, sprang.[93]

Access to the ARPANET was expanded in 1981 when the National Science Foundation (NSF) funded the Computer Science Network (CSNET).

Internetworking demonstration, linking the ARPANET, PRNET, and SATNET in 1977

The transatlantic connectivity with Norway (NORSAR and NDRE) and UCL later evolved into the SATNET. The ARPANET, SATNET and PRNET were interconnected in 1977. The DoD made TCP/IP the standard communication protocol for all military computer networking in 1980.[94] Norway and University College London left the ARPANET and began using TCP/IP over SATNET in 1982.[90] On January 1, 1983, known as flag day, TCP/IP protocols became the standard for the ARPANET, replacing the earlier Network Control Protocol.[95][15]

In September 1984 work was completed on restructuring the ARPANET giving U.S. military sites their own Military Network (MILNET) for unclassified defense department communications.[96][97] Both networks carried unclassified information and were connected at a small number of controlled gateways which would allow total separation in the event of an emergency. MILNET was part of the Defense Data Network (DDN).[98] Separating the civil and military networks reduced the 113-node ARPANET by 68 nodes. After MILNET was split away, the ARPANET would continue to be used as an Internet backbone for researchers, but be slowly phased out.

Applications

[edit]

NCP provided a standard set of network services that could be shared by several applications running on a single host computer. This led to the evolution of application protocols that operated, more or less, independently of the underlying network service, and permitted independent advances in the underlying protocols.[citation needed]

The various application protocols such as TELNET for remote time-sharing access and File Transfer Protocol (FTP), the latter used to enable rudimentary electronic mail, were developed and eventually ported to run over the TCP/IP protocol suite. In the 1980s, FTP for email was replaced by the Simple Mail Transfer Protocol and, later, POP and IMAP.[citation needed]

Telnet was developed in 1969 beginning with RFC 15, extended in RFC 855.[citation needed]

The original specification for the File Transfer Protocol was written by Abhay Bhushan and published as RFC 114 on 16 April 1971. By 1973, the File Transfer Protocol (FTP) specification had been defined (RFC 354) and implemented, enabling file transfers over the ARPANET.[citation needed]

In 1971, Ray Tomlinson, of BBN sent the first network e-mail (RFC 524, RFC 561).[12][99] An ARPA study in 1973, a year after network e-mail was introduced to the ARPANET community, found that three-quarters of the traffic over the ARPANET consisted of email messages.[100][101][102] E-mail remained a very large part of the overall ARPANET traffic.[103]

The Network Voice Protocol (NVP) specifications were defined in 1977 (RFC 741), and implemented. But, because of technical shortcomings, conference calls over the ARPANET never worked well; the contemporary Voice over Internet Protocol (packet voice) was decades away.[citation needed]

Security

[edit]

The Purdy Polynomial hash algorithm was developed for the ARPANET to protect passwords in 1971 at the request of Larry Roberts, head of ARPA at that time. It computed a polynomial of degree 224 + 17 modulo the 64-bit prime p = 264 − 59. The algorithm was later used by Digital Equipment Corporation (DEC) to hash passwords in the VMS operating system and is still being used for this purpose.[citation needed]

Rules and etiquette

[edit]

Because of its government funding, certain forms of traffic were discouraged or prohibited.

Leonard Kleinrock claims to have committed the first illegal act on the Internet, having sent a request for return of his electric razor after a meeting in England in 1973. At the time, use of the ARPANET for personal reasons was unlawful.[104][105]

In 1978, against the rules of the network, Gary Thuerk of Digital Equipment Corporation (DEC) sent out the first mass email to approximately 400 potential clients via the ARPANET. He claims that this resulted in $13 million worth of sales in DEC products, and highlighted the potential of email marketing.[citation needed]

A 1982 handbook on computing at MIT's AI Lab stated regarding network etiquette:[106]

It is considered illegal to use the ARPANet for anything which is not in direct support of Government business ... personal messages to other ARPANet subscribers (for example, to arrange a get-together or check and say a friendly hello) are generally not considered harmful ... Sending electronic mail over the ARPANet for commercial profit or political purposes is both anti-social and illegal. By sending such messages, you can offend many people, and it is possible to get MIT in serious trouble with the Government agencies which manage the ARPANet.

Decommissioning

[edit]

In 1985, the NSF funded the establishment of national supercomputing centers at several universities and provided network access and network interconnectivity with the NSFNET project in 1986. NSFNET became the Internet backbone for government agencies and universities.

The ARPANET project was formally decommissioned in 1990. The original IMPs and TIPs were phased out as the ARPANET was shut down after the introduction of the NSFNet, but some IMPs remained in service as late as July 1990.[107][108]

In the wake of the decommissioning of the ARPANET on 28 February 1990, Vinton Cerf wrote the following lamentation, entitled "Requiem of the ARPANET":[109]

It was the first, and being first, was best,
but now we lay it down to ever rest.
Now pause with me a moment, shed some tears.
For auld lang syne, for love, for years and years
of faithful service, duty done, I weep.
Lay down thy packet, now, O friend, and sleep.

-Vinton Cerf

Legacy

[edit]
ARPANET and related projects. Figure from 1990.[110]

The technological advancements and practical applications achieved through the ARPANET were instrumental in shaping modern computer networking including the Internet. Development and implementation of the concepts of packet switching, decentralized networks, and communication protocols, notably TCP/IP, laid the foundation for a global network that revolutionized communication, information sharing and collaborative research across the world.[111]

The ARPANET was related to many other research projects, which either influenced the ARPANET design, were ancillary projects, or spun out of the ARPANET.

Senator Al Gore authored the High Performance Computing and Communication Act of 1991, commonly referred to as "The Gore Bill", after hearing the 1988 concept for a National Research Network submitted to Congress by a group chaired by Leonard Kleinrock. The bill was passed on 9 December 1991 and led to the National Information Infrastructure (NII) which Gore called the information superhighway.

The ARPANET project was honored with two IEEE Milestones, both dedicated in 2009.[112][113]

On May 17, 2011, Arlington County, Virginia erected two historical markers commemorating the internet's roots, at 1400 Wilson Boulevard, in its Rosslyn neighborhood, the agency's home from 1970 to 1975.[114]

See also

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References

[edit]

Sources

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

ARPANET

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from Grokipedia
The ARPANET (Advanced Research Projects Agency Network) was the pioneering packet-switching network developed by the Department of Defense's Advanced Research Projects Agency () in the late 1960s, serving as the foundational precursor to the modern by enabling the interconnection and resource sharing among geographically dispersed computers. Its primary purpose was to facilitate secure communications, collaborative research, and efficient data exchange across military and academic sites, addressing the need for resilient networking in the face of potential disruptions like nuclear threats. Initiated under the vision of program manager , who conceptualized an "" in 1962, the project gained momentum through key contributions from figures like Lawrence Roberts, who oversaw its architectural design as IPTO director. Development began in earnest in fiscal year 1969 with DARPA's "Resource Sharing Computer Networks" program, leading to the installation of the first Interface Message Processors (IMPs)—early routers—by BBN Technologies. The network's inaugural milestone occurred on October 29, 1969, when the first message ("LO" as an attempt at "LOGIN") was successfully transmitted from a computer at the University of California, Los Angeles (UCLA) to the Stanford Research Institute (SRI), marking the birth of operational packet switching. By the end of 1969, ARPANET connected its initial four nodes: UCLA, the Stanford Research Institute, the University of California, Santa Barbara (UCSB), and the University of Utah, forming a foundational wide-area network that demonstrated distributed computing's viability. Expansion continued rapidly, with the Network Working Group (NWG) establishing protocols like the initial host-to-host protocol in 1971, and the first public demonstration at the International Computer Communication Conference in Washington, D.C., in 1972. A pivotal evolution came through the development of the Transmission Control Protocol (TCP) and (IP) by Vinton Cerf and Robert Kahn in the mid-1970s, which standardized data transmission and enabled interoperability among diverse networks. In July 1975, operational control of ARPANET shifted from to the Defense Communications Agency (now ), by which time it supported over 50 nodes spanning from to . The full transition to TCP/IP occurred on January 1, 1983—often called the "flag day" of the —allowing ARPANET to interconnect with other networks like those funded by the (NSFNET), thus birthing the broader . ARPANET was formally decommissioned in 1990 as its functions were fully absorbed into the expanding commercial and civilian infrastructure. ARPANET's innovations in , conceived partly from Paul Baran's earlier work on survivable communications, proved instrumental in transforming global information sharing, influencing subsequent systems like Telenet and international public data networks. Beyond its technical achievements, it fostered early applications such as electronic mail (invented in 1971 by ) and remote login, laying the groundwork for the and today's digital economy. Its legacy endures as a testament to DARPA's role in driving the "Information Revolution," with ongoing impacts in cybersecurity, distributed systems, and networked computing.

Origins

Historical Context and Inspiration

The tensions of the mid-20th century, exacerbated by the Soviet Union's launch of on October 4, 1957, created a profound sense of urgency in the United States regarding technological superiority and . This event, often termed the , revealed perceived gaps in American missile and space capabilities, prompting widespread public anxiety and political calls for bolstered defense research. In response, the U.S. government established the Advanced Research Projects Agency () on February 7, 1958, to centralize and accelerate high-risk, high-reward projects in defense technologies, including computing and communications systems. These investments marked a shift toward innovative, resilient infrastructures capable of withstanding potential nuclear threats, setting the stage for networked computing initiatives. A foundational vision emerged from J.C.R. Licklider's 1960 paper "Man-Computer Symbiosis," where he described an integrated "thinking center" of computers, libraries, and data systems connected via wide-band communication lines to enable seamless resource sharing and human-machine collaboration. Licklider, who became the first director of ARPA's Information Processing Techniques Office (IPTO) in 1962, expanded this into the concept of a "Galactic Network"—a globally interconnected array of computers allowing users anywhere to access data and programs interactively. This idea emphasized systems, where multiple users could simultaneously utilize a single computer's resources, fostering efficient interactive computing. By the mid-1960s, ARPA had actively funded such systems, including MIT's Project MAC in 1963, which developed the (CTSS) to support collaborative research and multi-user access. Parallel theoretical advancements addressed the need for robust networks amid nuclear risks. In 1964, at the proposed a distributed in his report "On Distributed Communications Networks," advocating for messages to be broken into standardized 1024-bit "message blocks" transmitted independently across redundant nodes using store-and-forward routing. This approach, with built-in redundancy (e.g., connectivity levels of 3–4), ensured the network could survive attacks by dynamically rerouting blocks around damaged components, prioritizing resilience over centralized vulnerabilities. Independently, in 1965, at the UK's National Physical Laboratory (NPL) conceived , dividing data into small packets for transmission via an "interface computer" at each node, with a focus on statistical multiplexing to achieve efficient bandwidth utilization by dynamically allocating resources based on demand. These concepts, though developed separately, converged on decentralized architectures that influenced ARPA's pursuit of survivable, resource-efficient networks.

Project Initiation and Funding

The ARPANET project was formally initiated within the Advanced Research Projects Agency's () Information Processing Techniques Office (IPTO), which had been established in 1962 under the leadership of to advance computer research and networking concepts. Licklider's vision of an "Intergalactic Network" laid the groundwork, but practical development accelerated after succeeded him as IPTO director in 1964 and Robert Taylor took over in 1966. Taylor, a strong proponent of resource-sharing networks, convinced ARPA Director Charles Herzfeld in February 1966 to allocate $1 million from existing ballistic missile defense funds to explore a connecting ARPA-sponsored research sites. In late 1966, Taylor recruited Lawrence Roberts from MIT's Lincoln Laboratory to serve as IPTO program manager for the network project, tasking him with overseeing technical planning and contractor engagement. Roberts, building on packet-switching ideas, organized a series of meetings in , including a key summer study group of contractors and experts, which recommended a distributed using interface message processors (IMPs) to connect heterogeneous computers. These recommendations shaped the project's direction, leading Roberts to publish an initial ARPANET plan in October that outlined resource sharing among systems. Funding escalated as the project gained momentum; the initial $1 million supported through , after which committed fuller budgetary resources, including a dedicated "Resource Sharing Computer Networks" program starting in fiscal year 1969. By mid-1968, Roberts issued a formal request for proposals (RFP) for development, emphasizing reliability and modularity. In 1968, selected Bolt, Beranek and Newman (BBN) to build the IMPs under a $1 million contract led by Frank Heart, marking the transition from to implementation. The project's organizational structure prioritized collaboration among ARPA's academic and industry partners, with UCLA and Stanford Research Institute (SRI) designated as the initial host sites for the first IMP installations in 1969 to demonstrate core connectivity. Taylor and Roberts ensured that key figures from IPTO, including input from Licklider's earlier influence, guided decisions to foster a decentralized, survivable network aligned with ARPA's defense-oriented goals.

Technical Development

Interface Message Processors and Hardware

The Interface Message Processors (IMPs), the foundational hardware nodes of the ARPANET, were designed and constructed by Bolt, Beranek and Newman (BBN) under a contract awarded by the Advanced Research Projects Agency (ARPA) in 1968. These devices were ruggedized versions of the Honeywell DDP-516 minicomputer, a 16-bit processor known for its reliability in harsh environments, equipped with 12,000 words (24 kilobytes) of core memory and a 0.96-microsecond cycle time. The DDP-516's compact design, roughly the size of a refrigerator, was augmented with custom high-speed modem interfaces for inter-IMP communications and 1822 interfaces for connecting to host computers, enabling the IMPs to serve as dedicated packet switches rather than relying on general-purpose hosts for network functions. At their core, IMPs handled essential network operations through a combination of hardware and software tailored for . They performed packet assembly and disassembly to break down host messages into fixed-size packets of up to 1008 bits, routed packets using dynamic software table lookups that adapted to changes every 0.64 seconds, detected errors via calculations on packet headers and data (taking approximately 2 microseconds per word), and implemented store-and-forward transmission to buffer and packets across the network. Each IMP supported up to four host connections via custom asynchronous bit-serial cables operating at speeds up to 100 kbps over distances of 2,000 feet, while inter-IMP links used leased lines initially rated at 50 kbps with Bell 201 or 301 modems. These functions ensured decentralized control, with no , as routing decisions were made locally based on estimated transit delays. The deployment of the first four IMPs marked the ARPANET's operational beginning in late 1969, with installations at the (UCLA) on September 1, at the Stanford Research Institute (SRI) on October 1, at the (UCSB) on November 1, and at the on December 5. These IMPs interconnected via the 50 kbps lines to form a small diamond-shaped , allowing initial testing of host-to-host communication. BBN engineers encountered significant challenges in achieving and reliability, as the hardware needed to 80 fixed-length packet buffers simultaneously while managing congestion through mechanisms like "quenching" signals to prevent overloads, all without mass storage and under constraints of the era's limited processing power. Handling out-of-order packet reassembly and duplicate detection further tested the system's robustness, requiring meticulous software-hardware integration to maintain uptime in a production environment. To expand access beyond host computers, BBN evolved the IMP design into the Terminal Interface Processor (TIP) in 1971, which supported direct connections for up to 63 asynchronous terminals at speeds from 75 bps to 19.2 kbps. The TIP, first deployed in September 1971, used similar Honeywell-based hardware but with expanded port expanders to interface multiple low-speed devices, enabling remote users to dial in via modems and interact with the network without dedicated hosts. This democratized ARPANET usage and highlighted the hardware's adaptability, paving the way for broader applications while addressing reliability issues through enhanced buffer management and error handling.

Initial Protocols and Software

The BBN 1822 protocol, specified in 1969, established the foundational interface for communication between host computers and Interface Message Processors (IMPs) in the ARPANET. The initial 1822 protocol used a 64-bit leader, which was expanded to a 12-byte (96-bit) leader in later revisions to accommodate additional fields, containing, among other fields, source and destination addresses (initially 8 bits each, later 16 bits), message type (8 bits), identifier (12 bits), and length indicators, followed by data up to 1008 bits for regular packets. The IMPs handled packet assembly, disassembly, and initial routing, while hosts were responsible for generating and interpreting these messages over a direct physical connection, typically via custom serial interfaces. Message types under the 1822 protocol encompassed regular data packets (type 0) for primary information transfer, control messages for , and specialized packets for error handling and flow control. Control messages included type 5 (RFNM, or Ready for Next Message) to signal that a host could accept another message, enabling basic flow control by limiting up to eight outstanding messages per virtual circuit before requiring acknowledgment. Other control types covered host status notifications, such as type 2 (host going down) and type 6 (dead host status). Error handling relied on messages like type 1 (error without ID), type 8 (error with ID), and type 9 (incomplete transmission), with type 4 (NOP, or no operation) packets used for , , or probing the link without data transfer. These mechanisms ensured reliable local delivery from host to IMP but deferred end-to-end reliability to higher-layer protocols. Host software implementations adhering to the 1822 protocol required custom interfaces to connect diverse computer systems to the IMPs, often incorporating teletype terminals (such as ASR-33 models) for initial user interaction and debugging. Early debugging tools included local terminal monitors for tracing message exchanges and basic performance logging, with sites like UCLA's Network Measurement Center developing rudimentary network analysis software to monitor IMP-host interactions. However, the protocol's limitations were evident: it provided no built-in end-to-end error correction or acknowledgments between remote hosts, relying entirely on IMPs for store-and-forward routing and local recovery, which constrained scalability and reliability across the network. The first operational 1822-compliant host software ran on UCLA's SDS Sigma 7 computer, equipped with the time-sharing operating system modified for network access, and SRI's SDS 940 computer, using a customized system. On October 29, 1969, these implementations enabled the inaugural host-to-host interaction, where a command from UCLA to SRI transmitted only "LO" before a system crash, marking the initial successful partial data exchange over the protocol.

Implementation and Expansion

First Connections and Testing

The inaugural connection of the ARPANET occurred on October 29, 1969, when graduate student Charley Kline, under the supervision of at the (UCLA), attempted to transmit the word "" from the UCLA Sigma 7 host computer to the Stanford Research Institute (SRI) SDS 940 host computer over the newly installed Interface Message Processors (s). The transmission succeeded only for the first two characters, "LO," before a software caused the system to crash, marking both the network's first message and its initial failure. A subsequent attempt on November 21, 1969, established the first permanent link between the UCLA and SRI s, successfully sending the full "" message and enabling reliable host-to-host communication using the 1822 protocol for IMP interactions. The initial four-node configuration formed the core of ARPANET's early operations, with 1 installed at UCLA in September 1969, IMP 2 at SRI in October 1969, 3 at the (UCSB) in November 1969, and 4 at the in December 1969. By December 5, 1969, the entire four-node network was operational. These nodes, connected via 50 kbps leased telephone lines spanning up to 400 miles, represented the first operational packet-switched network, allowing experimental resource sharing among diverse host computers including the SDS Sigma 7, SDS 940, IBM 360/75, and PDP-10. Early testing focused on verifying packet , recovery, and , employing IMP-embedded diagnostics and host-based protocols to simulate and measure round-trip times. Cross-country packet latency typically ranged from 1 to 2 seconds in initial evaluations, influenced by line propagation delays and early software limitations, though the design targeted sub-0.5-second averages under load. Challenges included frequent software crashes on host systems during high-load tests and occasional cable faults on leased lines, which IMPs mitigated through automatic rerouting and failure isolation, ensuring localized rather than network-wide disruptions during 1969-1970 demonstrations. A key public showcase occurred at the 1972 International Computer Communication Conference, where the four-node network demonstrated real-time applications like and remote , validating ARPANET's viability despite these teething issues.

Growth Phases and Milestones

The ARPANET experienced rapid expansion following its initial deployment, growing from a small experimental network to a robust system supporting widespread research collaboration. In , the deployment of the Terminal Interface Processor (TIP) marked a key milestone, allowing up to 64 remote terminals to connect directly to the network without dedicated host computers, thereby broadening access for users beyond the original institutional sites. In 1971, the network reached 15 nodes and 23 hosts, connecting institutions such as UCLA, Stanford Research Institute, and , which demonstrated its scalability for resource sharing. That year also saw the introduction of satellite links to , enabling the integration of the packet radio network and extending ARPANET's reach across oceanic distances for the first time. Building on the initial four nodes from , this phase emphasized reliable over diverse geographies. The year brought the network to approximately 37 nodes by year's end, reflecting accelerated adoption by academic and defense centers. A pivotal event was the first public demonstration at the International Conference on Computer Communications (ICCC) in , where graphical applications and real-time interactions were showcased via TIP-connected terminals, validating ARPANET's potential for interactive computing and drawing international attention to packet-switched networking. Capacity improvements continued in 1973 with the upgrade to 56 kbps lines, enhancing data throughput for growing traffic demands. That same year, international extensions were achieved through a satellite link to (UCL) in the UK via the Atlantic, following an initial connection to the Norwegian Seismic Array (NORSAR), which marked ARPANET's first transoceanic ties and foreshadowed global networking. By 1975, the network handled over 3 million packets daily, underscoring its operational maturity and the effectiveness of IMP hardware in managing increased loads. Further upgrades included the deployment of advanced IMP variants, such as the Pluribus and Satellite IMPs, to support higher capacities and diverse link types. A significant 1977 milestone was the of ARPANET with the satellite network and the PRNET network using gateway protocols, serving as a precursor to broader efforts that later influenced the NSFNET's development in the . This demonstration highlighted the feasibility of linking heterogeneous networks, paving the way for standardized protocols like TCP/IP.

Protocol Evolution

Network Control Protocol Era

The Network Control Protocol (NCP), introduced in 1970, served as the primary host-to-host communication protocol for ARPANET, replacing the initial ad-hoc procedures defined under the host-IMP interface to enable true end-to-end connections between remote hosts. Developed by the Network Working Group under , NCP was finalized in December 1970 following discussions outlined in RFC 1, which proposed early standards for host software including connection primitives and error checking. By 1971, ARPANET sites had begun implementing NCP, standardizing the network interface and facilitating the integration of additional hosts. NCP established virtual circuits through simplex connections identified by socket pairs—each socket comprising a host number and a 16-bit identifier—allowing processes on different hosts to communicate as if directly linked. It supported 8-bit byte-oriented data streams, enabling the transport of arbitrary data without the character-oriented restrictions of earlier systems. Flow control was managed through a credit-based , where receivers allocated credits (via sequence numbers and credit fields in acknowledgments) to senders, specifying the number of messages that could be sent to prevent receiver overload. These mechanisms underpinned higher-level protocols such as for remote login and the initial (FTP) for reliable data exchange, marking a shift from experimental connections to practical network usage across the growing ARPANET. Despite its advancements, NCP exhibited key limitations that became apparent as ARPANET expanded. It lacked support for , having been designed exclusively for the single ARPANET infrastructure with no provisions for across heterogeneous networks. Addressing was fixed to 16-bit socket numbers per host, which, while providing a large , lacked dynamic allocation and contributed to issues in practice due to implementation limits. Additionally, NCP was vulnerable to congestion, as it provided no end-to-end error or flow control beyond basic acknowledgments, assuming the underlying IMP network's reliability and leading to performance degradation during high loads. By 1973, these shortcomings prompted discussions on protocol evolution, with Robert Kahn and Vinton Cerf initiating planning to address NCP's inability to support emerging multi-network environments. This era of NCP dominance, spanning until its phase-out in 1982, solidified ARPANET's role in demonstrating packet-switched networking while highlighting the need for more robust, extensible designs.

Transition to TCP/IP

The development of the Transmission Control Protocol (TCP) began with the 1974 paper by Vinton Cerf and Robert Kahn, titled "A Protocol for Packet Network Intercommunication," which proposed a host-to-host protocol for interconnecting heterogeneous packet-switched networks like ARPANET. This initial TCP design combined transport and network layer functions into a single protocol, emphasizing reliable data delivery across diverse networks. Over the following years, iterative refinements led to the recognition that separating these functions would better support a modular, layered ; in 1978, TCP was split into the separate Transmission Control Protocol (TCP) for the and (IP) for the network layer, enabling more flexible . TCP provided reliable stream delivery through mechanisms such as sequence numbering, positive acknowledgments, and retransmissions to handle , ensuring data arrived in order and without errors. It incorporated flow and congestion control using a , where the sender could transmit multiple packets up to a dynamic window size before receiving acknowledgments, preventing network overload by adjusting to receiver buffer capacity and link conditions. For error detection, TCP employed a 16-bit covering the header, data, and a pseudo-header including source and destination addresses. Complementing this, IP handled 32-bit addressing to uniquely identify hosts across interconnected networks, supporting connectionless datagram where packets were forwarded independently based on destination addresses without establishing end-to-end connections. IP also managed fragmentation and reassembly, allowing large s to be broken into smaller pieces for transmission over networks with varying sizes and reassembled at the destination. Testing of the mature TCP/IP suite occurred in 1982 and 1983, with implementations developed for various systems, including ports to Unix-based environments like the Berkeley Software Distribution (BSD) under DARPA contracts awarded to organizations such as BBN. These trials validated interoperability and performance across ARPANET hosts, culminating in the Department of Defense's declaration of TCP/IP as the standard protocol suite in March 1982. On January 1, 1983—known as "flag day"—ARPANET fully transitioned from the Network Control Protocol to TCP/IP, requiring all hosts to adopt the new suite simultaneously to maintain connectivity. This switchover not only stabilized ARPANET operations but also facilitated its interconnection with other networks, such as the satellite-based SATNET, forming the foundation of a proto-Internet by enabling seamless data exchange across diverse packet-switched systems.

Operations and Applications

Network Management and Usage

The Network Information Center (NIC), established at Stanford Research Institute (SRI) and directed by Elizabeth Feinler from 1972 onward, served as the central hub for ARPANET's administrative functions. The NIC maintained comprehensive host tables that mapped network addresses to hostnames, facilitating connectivity across the growing number of nodes, and distributed (RFC) documents to document protocols and standards. Additionally, it provided directory services through publications like the ARPANET Directory, which acted as an electronic phonebook listing users, resources, and contact information, supporting the collaborative research environment. Under Feinler's leadership, the NIC evolved from a small team handling basic documentation to a robust operation distributing tens of thousands of documents annually and registering new hosts. Network monitoring was primarily handled by the Network Measurement Center (NMC) at UCLA, established in 1969 under , which conducted ongoing to evaluate performance and identify bottlenecks. The NMC collected statistics on packet flows, delays, and utilization, revealing exponential traffic growth from 1971 to 1973 that strained the 50 kbps leased lines. Performance metrics indicated average throughputs of 10-20 kbps during typical operations, influenced by protocol overhead and routing dynamics, which informed adaptive improvements to sustain reliability. Access to ARPANET was strictly limited to institutions and researchers funded by the Advanced Research Projects Agency (), ensuring the network supported defense-related computing and academic collaboration without broader public involvement. By , the network connected over 100 hosts, serving approximately 1,000 users primarily at universities and research labs, with hosts required to implement compatible software for connection. Usage patterns emphasized resource sharing for computation and data exchange, monitored through the NIC to prevent overload. A notable operational incident occurred in 1975 amid rapid expansion, when surging traffic—doubling every 20 months—led to widespread congestion, prompting the transfer of management from to the Defense Communications Agency (DCA) for enhanced oversight. Recovery procedures involved localized IMP diagnostics, automatic code reloads for failures, and algorithm tweaks to routing and flow control, minimizing downtime to hours rather than days. These measures restored stability, allowing continued growth while addressing the crisis triggered by unchecked demand. Resource allocation relied on bandwidth sharing through the Network Control Protocol's (NCP) type-of-service field, which assigned priority levels to packets, enabling differentiation between routine academic traffic and higher-priority military communications. Adaptive algorithms dynamically balanced loads across links, ensuring equitable distribution without dedicated channels, though military traffic increasingly dominated by mid-1970s, influencing later network partitioning. This approach maintained overall utilization at 20-40% of capacity, prioritizing resilience over guaranteed rates.

Key Applications and Innovations

One of the most transformative applications developed on ARPANET was electronic mail, pioneered by in late 1971 while working at Bolt, Beranek and Newman (BBN). Tomlinson extended local messaging programs, SNDMSG for sending messages and READMAIL for retrieving them, by integrating them with an experimental file-transfer utility called CPYNET to enable messages to be sent between computers on the network. He introduced the "@" symbol to denote the user's location at a specific host, creating the foundational email addressing format that persists today. This innovation quickly gained popularity among ARPANET users, with Tomlinson's system deployed to other sites by 1972, fundamentally altering communication by allowing asynchronous, networked exchanges independent of physical presence. By 1973, email accounted for approximately 75% of all ARPANET traffic, underscoring its profound influence on network utilization. The File Transfer Protocol (FTP), specified in 1973, further enhanced ARPANET's utility by standardizing the efficient transfer of files between remote hosts, promoting resource sharing across the network. Developed under the Network Working Group, FTP built on earlier file transfer experiments and was detailed in RFC 454, which outlined commands for uploading, downloading, and managing files while handling differences in host file systems. This protocol enabled researchers to access and exchange data sets, software, and documents seamlessly, reducing duplication of efforts and accelerating collaborative projects in fields like computer science and physics. Telnet, formalized around the same period in 1973 as part of ARPANET's Network Control Protocol suite, provided a mechanism for , allowing users to interact with distant computers as if they were locally connected. Specified in documents like RFC 318 from 1972 and refined in subsequent updates, supported virtual terminal emulation, enabling multi-user sessions where operators could execute commands, run programs, and debug systems on remote machines over the network. This capability was essential for environments, permitting experts to leverage specialized hardware without travel. Early recreational applications also emerged, demonstrating ARPANET's potential for interactive entertainment. Ports of the pioneering game Spacewar!, originally developed in 1962 at MIT, were distributed across ARPANET nodes starting around 1970 when connected to the network, with widespread play and adaptations by 1972 that adapted the two-player space combat simulation to various systems. By 1980, more sophisticated multiplayer experiences appeared on ARPANET, including access to the first —a text-based adventure game created in 1978 by Roy Trubshaw and at the —which allowed simultaneous players from ARPANET-connected sites to explore a shared fantasy world, foreshadowing modern online gaming. A key success in resource sharing was the remote access to supercomputers like the , an ARPA-funded massively parallel system at the University of Illinois, which became available via ARPANET starting in 1975 after its relocation and integration. This enabled distributed researchers to submit jobs and retrieve results from the 's 64 processing elements without on-site presence, exemplifying ARPANET's goal of equitable access to resources and supporting applications in simulations, , and scientific modeling.

Security and Policies

Security Challenges and Responses

In the , ARPANET encountered significant challenges stemming from its foundational design and operational environment. The network's packet-switched transmitted unencrypted data over leased lines, making interception feasible by adversaries with access to those lines. Additionally, insider access risks arose due to the network's open participation model, which connected sites with academic institutions and encouraged broad collaboration among researchers, often without robust mechanisms to prevent misuse by authorized users. This collegial approach, while fostering innovation, exposed sensitive and research data to potential internal threats from students, faculty, or other participants. Early responses to these vulnerabilities focused on basic access controls implemented in the . Network administrators relied on simple password-based to verify users. The Network Information Center (NIC) at maintained host tables—centralized lists of authorized machines and their addresses—to regulate connections and prevent unauthorized logins. These measures provided initial barriers but were limited by weak password policies and the potential for table manipulation, offering only partial protection against determined insiders or external probes. By the early , escalating concerns over classified traffic prompted structural changes, including the 1983 split of ARPANET into two networks: the civilian-focused ARPANET for research and for unclassified Department of Defense (DoD) communications. This division, executed by the Defense Communications Agency, isolated military nodes—reducing ARPANET from 113 to 45 nodes—and incorporated gateways for limited exchange, thereby containing potential breaches within the more secure environment. DoD security policies evolved concurrently to address these issues, drawing influence from emerging standards like the (TCSEC), commonly known as , finalized in 1985. established hierarchical evaluation classes (from D, minimal protection, to A1, verified protection) for computer systems handling sensitive data. Complementing these were experiments, including ARPA-NSA collaborations on private line interfaces for end-to-end data protection and the BLACKER front-end system tested in the mid-1980s to enable secure interconnections between networks of varying classification levels. Incident handling improved in the 1980s, exemplified by responses to events like the October 1980 ARPANET crash, which affected 73 nodes due to a software bug in the NCP protocol, leading to enhanced monitoring and protocol improvements. These efforts, often conducted in partnership with DoD agencies, resulted in targeted patches and policy mandates for regular vulnerability assessments to safeguard military and research integrity.

Rules, Etiquette, and Governance

The rules and governing ARPANET usage emerged as informal guidelines and formal policies to ensure the network's sustainability for purposes, reflecting its origins as a U.S. Department of Defense-funded project under oversight. Early user behavior was shaped by the need to conserve limited bandwidth and computational resources, leading to memos and documents that promoted responsible conduct. These norms evolved alongside the network's growth, transitioning from advice in the 1970s to more structured prohibitions in the 1980s, while structures provided centralized coordination and . A key document outlining netiquette appeared in 1982 with the publication of "Getting Started Computing at the AI Lab," a from MIT's Artificial Intelligence Laboratory that emphasized relevance in communications to avoid wasting network resources. It advised users to limit messages to government business or research, noting that personal communications were acceptable but commercial or political uses were prohibited. This guidance was particularly important for and file transfers, the primary applications driving user interaction, and it underscored the network's experimental nature by warning that misuse could lead to restricted access. The handbook's principles aligned with broader ARPANET documentation efforts, helping to foster a culture of considerate usage among researchers. Formal policies were codified in the Acceptable Use Policy (AUP), which prohibited commercial activities to maintain the network's focus on non-profit research and government-related tasks, as enforced by ARPA. This restriction stemmed from ARPANET's funding mandate, ensuring resources were dedicated to advancing computer science and defense applications rather than private enterprise; violations could result in termination of access by ARPA administrators. The AUP reflected the era's view of the network as a shared public good, similar to library resources, and was communicated through official directives and user agreements at connected institutions. Governance of ARPANET was primarily handled by ARPA's Information Processing Techniques Office (IPTO), which directed funding, technical standards, and overall policy implementation, while the Network Information Center (NIC) at Stanford Research Institute served as a central hub for user support and mediation. The IPTO, led by figures like Robert Taylor, coordinated with contractors such as BBN Technologies to enforce operational rules and allocate , ensuring alignment with ARPA's strategic goals. The NIC, operational since 1970, maintained protocol documentation, host registrations, and an archive of (RFCs), while also mediating disputes over access, protocol interpretations, or through informal consultations and advisory memos. This dual structure allowed for agile decision-making in a decentralized environment, preventing major conflicts from disrupting network operations. Etiquette norms evolved in response to practical challenges, beginning with 1970s memos urging users to avoid congestion through efficient resource use, such as limiting file transfers during peak hours and prioritizing research data over personal communications. For instance, early RFCs and NIC bulletins from the mid-1970s highlighted the risks of network overload, recommending staggered logins and minimal retransmissions to sustain performance across the growing number of nodes. By the , these guidelines hardened into explicit bans on disruptive behaviors, including chain letters, which were deemed contrary to DoD policy for consuming bandwidth without advancing research objectives; a 1982 advisory explicitly condemned such practices after outbreaks of viral messages. This progression mirrored the network's maturation, with serving as a self-regulatory mechanism to complement technical safeguards. The formation of user communities further reinforced these norms, exemplified by the Network Working Group (NWG) established in to facilitate collaboration and feedback on network usage. This group brought together researchers from universities and labs to discuss , share best practices, and influence policy through meetings and RFC contributions, thereby embedding cultural expectations of mutual respect and efficiency into the ARPANET's fabric.

End and Legacy

Decommissioning Process

In 1989, the U.S. Department of Defense (DoD), through the Defense Communications Agency (DCA), decided to phase out ARPANET due to the widespread success of the TCP/IP protocol suite and the rapid expansion of the , which provided a more scalable alternative for research and academic connectivity. This decision marked the end of ARPANET's primary role, as its original infrastructure had become obsolete in supporting the growing demands of interconnected networks. The official decommissioning occurred on February 28, 1990, when the last data packets were routed over the network, effectively shutting down its operations after more than two decades of service. The process involved a coordinated wind-down managed by the DCA, ensuring minimal disruption to ongoing activities. As part of the transition strategy, ARPANET users were migrated to NSFNET for non-military academic and purposes, while military traffic was redirected to the existing , which had been separated from ARPANET in 1983. Remaining assets, including Interface Message Processors (IMPs) and associated hardware, were either repurposed for other DoD projects or decommissioned. By 1989, the broader ecosystem ARPANET helped spawn had grown to over 100,000 hosts, reflecting its foundational influence. The end was marked by ceremonial events, including a at UCLA in 1989 that commemorated ARPANET's 20th anniversary and highlighted its contributions to networking. Archival efforts focused on preserving key artifacts, with institutions like UCLA establishing dedicated collections of network logs, records, and original hardware to document ARPANET's operational history. These preservation initiatives, including the Heritage Site and Archive, ensure that logs from the first transmissions and progress reports to remain accessible for historical study.

Long-Term Impact and Influence

ARPANET served as the direct precursor to the modern Internet through the standardization of TCP/IP protocols, which replaced the earlier Network Control Program on January 1, 1983, enabling the interconnection of diverse networks on a global scale. This transition, often called "Flag Day," marked the birth of the Internet as a decentralized system capable of linking ARPANET with other networks like those funded by the National Science Foundation, fostering widespread adoption beyond military and academic use. The protocol's open architecture, developed by Vinton Cerf and Robert Kahn, allowed for scalable, interoperable communication, laying the groundwork for the Internet's expansion into a ubiquitous global infrastructure. Key innovations from ARPANET profoundly shaped contemporary networking. Its implementation of , the first operational wide-area packet-switched network, broke data into discrete packets routed independently, providing resilience and efficiency that became the foundational mechanism of the . Additionally, ARPANET birthed early systems, with protocols evolving into the (SMTP) still used today for message delivery across networks. These advancements prioritized distributed control and resource sharing, influencing core Internet standards. On a socio-economic level, ARPANET catalyzed the of information by enabling rapid, collaborative access to research data among distant institutions, sparking an information revolution that extended to civilian applications. This networked foundation indirectly enabled precursors to the , such as Tim Berners-Lee's 1989 proposal for hypertext systems at , which built upon protocols to make information universally accessible via browsers and hyperlinks. The resulting global connectivity transformed economies, education, and communication, shifting power from centralized entities to distributed users. ARPANET's legacy is recognized through prestigious awards, notably the 2004 A.M. granted to Vinton Cerf and Robert Kahn for their design of TCP/IP, hailed as the "Nobel Prize of computing" for enabling the Internet's foundational architecture. Its influence persists in modern cybersecurity doctrines, where ARPANET's early development of firewalls and fault-tolerant routing addressed vulnerabilities in distributed environments, informing contemporary defenses against network threats. Similarly, it pioneered distributed systems through programs like in the , which demonstrated self-propagating software across nodes, shaping resilient computing paradigms used in and architectures today.

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  29. https://blog.cloudflare.com/fifty-years-ago/
  30. https://www.lk.cs.ucla.edu/internet_first_words.html
  31. https://www.icann.org/en/blogs/details/the-first-message-transmission-29-10-2019-en
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  33. https://www.sri.com/75-years-of-innovation/75-years-of-innovation-arpanet/
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  35. https://historyofdomainnames.com/leonard-the-history-of-domain-names/
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  39. https://www.computerhistory.org/internethistory/1970s/
  40. https://www.livinginternet.com/i/ii_ncp.htm
  41. https://www.rfc-editor.org/rfc/rfc1.txt
  42. https://www.rfc-editor.org/rfc/rfc714.txt
  43. https://www.cs.princeton.edu/courses/archive/fall16/cos561/papers/JustWorks06.pdf
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  45. https://www.cs.princeton.edu/courses/archive/fall20/cos461/papers/TCPIP74.pdf
  46. https://datatracker.ietf.org/doc/html/rfc2235
  47. https://www.comsoc.org/node/19651
  48. https://datatracker.ietf.org/doc/html/rfc791
  49. https://historyofcomputercommunications.info/section/11.8/TCP-IP-and-XNS-1981-1983/
  50. https://www.internetsociety.org/blog/2016/09/final-report-on-tcpip-migration-in-1983/
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  53. https://ui.adsabs.harvard.edu/abs/1977ITCom..25...95K/abstract
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  55. https://www.sri.com/hoi/domain-names-the-network-information-center/
  56. https://datatracker.ietf.org/doc/rfc810/
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  58. https://www.computerhistory.org/internethistory/1980s/
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  64. https://www.clir.org/pubs/reports/evolv/appendix/
  65. https://www.tandfonline.com/doi/full/10.1080/23738871.2016.1157619
  66. https://www.nsf.gov/impacts/internet
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  74. https://amturing.acm.org/award_winners/cerf_1083211.cfm
  75. https://www.spiceworks.com/tech/networking/articles/what-is-arpanet/
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